We have just linked in auto-complete of shares with contacts. Now when you go to share a page the contacts you have already created earlier in the job are able to be selected without having to retype their details.
Clicking the name you wish to use will populate the email address as well. You may still type new names and addresses as before but if the person is likely to be someone you will be sharing a number of pages with go to the contacts tab and set them up in there first:
For more about sharing pages see here.